When a patient is to receive radiation treatment, the patient needs to be carefully aligned with the iso-center of the radiation beam. Typically, tissue to be treated is identified and localized during treatment planning. Then, later during treatment sessions, the task is to reproduce the exact position as during the planning session.
A variety of techniques can be used for patient positioning Frequently some automatic registration procedure is deployed to recover the transformation that needs to be applied to the treatment couch to perform the alignment. However, it is typically the case that all planning data except the required position is ignored. This results in decreased accuracy of the automatic aligning. The root of the problems with the accuracy lies in the fact that all data points in a planning volume and a treatment volume are used equally when computing a mean square error (MSE).